Many different applications for coating of fibers are known. One way to coat a fiber is by chemical vapor deposition or "CVD".
Conventional coating of a fiber starts with a portion of the fiber called a core being heated by a direct electrical current through the fiber. The hot core is exposed to reagent vapor, to be coated by CVD. The core can be simultaneously spooled through a chamber containing reagent gases. The current is introduced into the chamber via mercury electrodes that also serve as gas seals for the ends of the reaction chamber. Each chamber can typically accommodate only a single fiber at a time.
Such a system has drawbacks. The toxic character of the mercury that is used in the electrodes becomes an environmental hazard. Moreover, many systems allow only a single fiber to be processed at a time. This can be expensive in terms of production costs. These systems also require that the fiber be at least a moderately good electrical conductor in order to achieve adequate heating for the CVD.
European Patent No. 0552951A1 describes coating fibers using CVD in a microwave heating of a waveguide applicator. This system operates without mercury and extends the range of fiber materials. However, this system is limited. For example, this system does not teach how to coat more than a single fiber at a time.